The president is free to call news “fake” and to blast the media. That goes against convention, but it is not unconstitutional. But a demand to cease and desist publication—a clear effort by the President of the United States to intimidate a publisher into halting publication of an important book on the workings of the government—is an attempt to achieve what is called prior restraint. That is something that no American court would order as it is flagrantly unconstitutional.
This is very clearly defined in Supreme Court case law, most prominently in the Pentagon Papers case.
I haven’t read the book and have no opinion about it, but I’m glad to see the publisher stand up for Americans’ rights.